---
id: incremental
title: 增量渲染
---

### 示例

```jsx live
function render(props) {
  const CHUNK_COUNT = 10;

  const container = useRef(null);

  const dataUrl = useBaseUrl('/examples/incremental/data/links_ny_{idx}.bin');

  const initChat = (map, option) => {
    const chart = new EChartsLayer(option, {
      hideOnMoving: true,
      hideOnZooming: true,
    });

    const fetchData = async (idx) => {
      if (idx >= CHUNK_COUNT) {
        return;
      }
      const url = dataUrl.replace('{idx}', idx);
      const d = await fetch(url).then((res) => res.arrayBuffer());

      const rawData = new Float32Array(d);
      const data = new Float64Array(rawData.length - 2);
      const offsetX = rawData[0];
      const offsetY = rawData[1];
      let off = 0;
      for (let i = 2; i < rawData.length;) {
        const count = rawData[i++];
        data[off++] = count;
        for (let k = 0; k < count; k++) {
          const x = rawData[i++] + offsetX;
          const y = rawData[i++] + offsetY;
          data[off++] = x;
          data[off++] = y;
        }
      }
      chart.appendData({
        seriesIndex: 0,
        data,
      }, true);
      fetchData(idx + 1);
    }

    fetchData(0);

    chart.appendTo(map);
  };

  const init = async () => {
    const map = new ol.Map({
      target: container.current,
      view: new ol.View({
        projection: 'EPSG:4326',
        zoom: 10,
        rotation: 0,
        center: [-74.04327099998152, 40.86737600240287],
      }),
      layers: [
        new TileLayer({
          source: new XYZ({
            url: 'https://{a-c}.basemaps.cartocdn.com/dark_all/{z}/{x}/{y}.png',
          }),
        }),
      ],
    });

    const option = {
      progressive: 20000,
      backgroundColor: 'transparent',
      series: [
        {
          type: 'lines',
          blendMode: 'lighter',
          dimensions: ['value'],
          data: new Float64Array(),
          polyline: true,
          large: true,
          lineStyle: {
            color: 'orange',
            width: 0.5,
            opacity: 0.3,
          },
        },
      ],
    };

    initChat(map, option);

    function resize(target) {}

    return {
      resize,
    };
  };

  useEffect(() => {
    const { resize } = init();

    return () => {};
  }, []);

  return (
    <div className="live-wrap">
      <div ref={container} className="map-content" />
    </div>
  );
}
```
